The Drosophila Genome Project has as one of its goals correlating the physical and genetic maps of the Drosophila genome. This involves the identification of all the genes in the Drosophila genome, not only at the DNA sequence level, but at the functional level as well. To accomplish this goal, mutations must be identified in all genes whose functions are vital to the organisms development and reproduction and these genes must be correlated with specific transcription units and DNA sequences. Current methods for the identification and cloning of Drosophila genes rely heavily on the use of P element insertional mutagenesis and chemical mutagenesis. Although these methods provide invaluable tools for genetic analysis of the genome, it is clear that other methods are needed. This research has as its primary goal the development of a new method to use in the genetic and molecular analysis of the Drosophila genome - the construction of extended P elements containing large (100-500 kb) chromosomal regions between two compatible, functional P ends. Extended P elements will be made by manipulation of existing P element insertions in vivo. A genetic screen has been developed that identifies P element deletion derivatives having lost one of the two ends of the P element required for transposition. The placement of two such half-P elements a known distance apart on the same chromosome creates an extended P element. These extended P elements will be characterized with respect to the observed frequency of transposition and excision, the spectrum of transposase-mediated events obtained, and the effect of P element size on these events. Extended P elements have tremendous potential as tools for the genetic analysis of the Drosophila genome. Potential applications include (1) generations of a set of end to end transpositional duplications covering most of the genome; and (2) generation of overlapping deficiencies by partial deletion of sequences between the P ends. If extended P elements are found to undergo excision, excision repair, and transposition at detectable frequencies, then the systematic application of the methods described can lead to the construction of a genomic set of extended P elements that could be used to identify most of the lethal complementation groups in the Drosophila genome and place them on the physical map of the genome.